This is a continuous effort in response to the increasing demand for a more precise measurement of relevant genomic information in any viral infection. The knowledge of the presence of specific viral genes will help in identifying the infectious agent. However, to assess the stage of a disease, to evaluate the efficacy of a treatment, to determine the value of a predictor in the progression of a disease, and to monitor progression of the patients infection, a more precise and quantitative analysis of the specific gene would be required. These previously highly research-oriented questions can now begin to be answered routinely in the clinical laboratories with advanced technology of molecular biology, such as polymerase chain reaction (PCR), and sequencing and mapping of the restriction nuclease digested fragments. We initiated developmental research in molecular diagnostic technology to meet our clinical study need. The demand for molecular testing of blood products for HIV, HCV, and HBV has grown. Whenever possible, we would improve the basic PCR technique to become a semi-quantitative procedure. During the last few years, we were able to apply PCR as the primary study tool for viral infection such as HG virus and TT virus. We found that these viruses are transmissible by blood transfusion but cause little or no hepatitis. We also initiated a project to construct an internal standard to be used in RT/PCR for determin-ing HCV RNA. A project to study the unique specificity of repairing enzyme, Mut Y, and its clinical application was also initiated as a collaborative project with the University of Mary-land. Our future effort in this program will be to continue to evaluate new testing approaches and specifically concentrate on perfecting the quantitation procedures, standardization, and application of molecular testing to blood products.